1. Field of the Invention
The present invention relates to an improvement in a multi-plate friction clutch comprising: a clutch outer; a clutch inner surrounded by the clutch outer; a plurality of first friction plates which are axially slidably spline-coupled to the clutch outer; a plurality of second friction plates which are superposed alternately with the first friction plates and axially slidably spline-coupled to the clutch inner; a pressure-receiving plate fixed to the clutch outer to be opposed to one side of a group of the first and second friction plates; and a clutch piston which is fitted to the clutch outer and which is capable of being hydraulically operated to press the group of the first and second friction plates toward the pressure-receiving plate, the clutch piston having a pressing surface adapted to press the group of the first and second friction plates and an annular retaining groove formed in the pressing surface, and a buffering Belleville spring being accommodated in the retaining groove and capable of resiliently abutting against the group of the first and second friction plates.
2. Description of the Related Art
A conventional multi-plate friction clutch is already known, as disclosed in Japanese Patent Application Laid-open No. 4-341652.
In the conventional multi-plate friction clutch, an inner peripheral surface of the retaining groove in the clutch piston is formed into a cylindrical surface coaxial with the clutch piston in order to facilitate the insertion of the Belleville piston into the retaining groove.
In the conventional multi-plate friction clutch, a total gap between the clutch piston and the pressure-receiving plate is set to prevent the falling-off of the Belleville spring from the retaining groove.
However, a gap between the adjacent friction plates cannot be narrowed to a given value or less in order to avoid the dragging of the clutch in a transmission cut-off state. Therefore, when the number of the friction plates is increased to increase the torque capacity of the clutch, it may be difficult in some cases to suppress the total gap between the clutch piston and the pressure-receiving plate to a range which prevents the disengagement of the Belleville spring.